(1) Field of the Invention
This invention relates to an electrophotographic photosensitive material. More particularly, it relates to an electrophotographic photosensitive layer containing an organic photoconductor and a polymeric binder.
(2) Description of the Prior Art
Organic photoconductors are advantageous over inorganic photoconductors in that they are light in weight, possess good flexibility, provide photosensitive layers excellent in transparency and can easily be combined into a composite material with other materials. Polyvinyl carbazoles, oxadiazoles and pyrazoline derivatives are known as such organic photoconductors.
Basic properties required for electrophotographic photosensitive materials are high static charge acceptance and high charge retentivity in the dark, a high sensitivity, a low residual voltage, a broad spectral sensitivity in the visible region, a high durability, no toxicity, and good processabilities (including a good film-forming property, a high transparency, a high flexibility and a good adaptability to the mass production. Organic photoconductors and inorganic photoconductors, which are satisfactory in all of these basic properties when they are used alone, have not heretofore been proposed. Thus, photoconductors popularly used at present have some defects or others.
Under this circumstance, function-separated electrophotographic photosensitive materials have recently been proposed. These photosensitive materials are based on the concept that the photosensitive layer is divided into layers differing in the function, that is, a charge generating layer for generating charges on absorption of light and a charge transport layer for transporting the formed charges, whereby the range for the selection of materials is broadened and some or all of the basic properties required for electrophotographic photosensitive materials are sufficiently manifested. Many function-separated electrophotographic photosensitive materials have heretofore been proposed, but only a limited number of them have been put into practical use. The practically used photosensitive materials still have some defects or others.
The combination of a charge generating material and a charge transport material has not theoretically been examined, but various combinations have been examined according to trial-and-error procedures.
The use of pyrazoline and hydrazone derivatives is described in U.S. Pat. No. 3,180,729, U.S. Pat. No. 3,837,851 and U.S. Pat. No. 4,150,987. However, hydrazine used as the starting material in these conventional techniques has a strong toxicity. Furthermore, U.S. Pat. No. 3,066,023 teaches the use of acylhydrazones. However, an electrophotographic photosensitive material comprising an acylhydrazone as the organic photoconductor has a problem such that the sensitivity is low.